Dimensionally stabilized wood and method of making such wood

ABSTRACT

1,164,689. Dimensionally stabilised wood. MO OCH DOMSJO A.B. 25 Aug., 1967 [26 Aug., 1966], No. 39301/67. Heading D1P. Wood is treated with 10-25% of polyalkylene glycol and 0.5-20% of glyoxal as an aqueous or organic solvent solution. The glycol may be diethylene, triethylene, dipropylene, or tripropylene glycol. The glyoxal (which effects cross-linking) may be in the form of glyoxal-sodium bisulphite or partially polymerised glyoxal. A catalyst, e.g. acetic or sulphuric acid or sodium bisulphate, may be used. The solution may also contain methyl, carboxymethyl, hydroxyethyl, methyl-hydroxyethyl, ethyl-hydroxyethyl, or ethyl-hydroxypropyl cellulose; polyvinyl alcohol; collagen; or casein. The moisture content of the wood being treated may exceed the fibre saturation point. Treatment may be by spraying or vacuum and/or pressure immersion.

United States Patent 3,547,679 DIMENSIONALLY STABILIZED WOOD AND METHOD OF MAKING SUCH WOOD Rolf Erhard Moren, Alfredshem, Sweden, assignor to M0 och Domsjo Aktiebolag, Ornskoldsvik, Sweden, a corporation of Sweden No Drawing. Filed Aug. 23, 1967, Ser. No. 662,576 Claims priority, application Sweden, Aug. 26, 1966, 11,578/ 66 Int. Cl. B27k 3/50, 3/02 U.S. Cl. 117-57 10 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to wood which is dimensionally stabilized by means of a special combination of treatment chemicals, and also to a method of making such dimensionally stabilized Wood.

It is known to treat wood with polyalkylene glycols to render it dimensionally stable. When the wood is to be dried, this treatment also results in an increased yield, because the wood can be retained in a swelled state without shrinking. This also has the advantage that drying can be carried out without any danger of qualityreducing checks occurring.

It is also known to treat wood chemically to achieve cross-linking between chemically reactive components thereof. By this method, the hydrophilic hydroxyl groups of the cellulose and lignin molecules may be replaced with less hydrophilic groups by a chemical treatment. The most simple and inexpensive method of forming cross-linkages in wood consists in heat-treating it at an elevated temperature, and by this treatment its tendency of swelling and shinking can be reduced by about 50%. The hygroscopicity of the Wood is also reduced correspondingly as compared to untreated wood. However, heat treatment of wood has not obtained practical use to any substantial extent, due to the fact that the wood becomes brittle and other mechanical characteristics thereof are also impaired. Another chemical method of achieving cross-linkages comprises treating the wood aldehyde vapours, primarily formaldehyde, in the presence of a mineral acid which acts as a catalyst. As a result of such treatment the wood will obtain a good dimensional stability at an increase in Weight of about 5%. However, the treatment with formaldehyde also results in a reduction of the mechanical characteristics of the wood, and the wood becomes brittle, wherefore this method has not been used in practice on a major scale.

The present invention relates to a method which removes the above disadvantages. According to the invention this method comprises carrying out stabilization by cross-linking with glyoxal and simultaneously swelling the wood with polyalkylene glycols or derivatives thereof. It was found, surprisingly, that by means of this invention it is possible to stabilize wood with a considerably reduced amount of chemicals as compared to treatment with polyalkylene glycols alone, and at the same time the undesirable brittleness which results from treatment with aldehyde alone, is eliminated.

In the treatment of this invention which is preferably carried out on wood having a moisture content exceeding the fiber saturation point, glyoxal is supplied by dipping the wood into a solution of glyoxal and polyalcohol in water or other solvent or by spraying or brushing the solution on the wood. Impregnation in vacuum and/or superatmospheric pressure can also be employed. In the subsequent drying of the wood, the portion of the glyoxal which has not been consumed to form cross-linkages between cellulose or lignin mole cules of the wood, will be hydrated and polymerized to form a mixture of hydrates of the formulae.

where n is an integer of the order of from 1 to 100.

These hydrates will function in the same manner as, e.g. polyethylene glycol in the treatment of the wood and will have a swelling action on the cell tissues, because the molecules are not greater than that they are capable of diffusing into the Wood.

Due to this combined effect, there will be needed e.g. for complete swelling of beechwood only an amount of about 15% of glyoxal and polyethylene glycol, based on the dry wood, while otherwise an amount of about 30% is necessary, when polyethylene glycol is used alone.

When drying wood treated with a combination of glyoxal and polyalkylene glycol, the polyalkylene glycol will react to some extent with glyoxal at elevated drying temperatures to form linear polyacetals, which may be tag. of the following composition, when the polyalkylene glycol is polyethylene glycol: Ho(o2H,oC2H4)..0oH-o(o2H,oozH4)n-oCHo Ho(o2H,-oo2Hr).0CHo(o2Hi-o-o2Hr)..o-oH0- Surprisingly, these products have also been found to have a dimensionally stabilizing effect on wood and other celluloisc materials, although they remain soluble in water.

Apart from the reduced consumption of polyalkylene glycol, the advantage is obtained that the wood, when it is fully impregnated, will obtain an improved surface which does not feel greasy. Also, its tendency of taking up moisture is.reduced. On the other hand, it is softer and smoother than wood treated with glyoxal alone as the stabilizing agent.

It is also contemplated, within the scope of this invention, to add to a wood impregnating liquid according to the invention other water-soluble substances, with which glyoXal reacts to form cross-linkages and which are thus rendered less soluble in water, whereby an improved reticulation in the cell structure is obtained. Examples of such substances which can either be caused to diffuse into the cell tissues or be deposited in the cell cavities, include water-soluble cellulose derivatives, such as hydroxyethylcellulose, ethyl-hydroxyethylcellulose, methylhydroxyethylcellulose, methylcellulose, ethylhydroxypropylcellulose, carboxymethyl cellulose, as well as other polymeric compounds, such as polyvinyl alcohol and partially hydrolyzed polyvinyl acetate, and also collagen and casein. Particularly suitable for addition in this manner are water-soluble cellulose derivatives having a viscosity below 20 cp. in 2% aqueous solution at 20 C.

Polyalkylene glycols and derivatives thereof which can be according to this invention, include e.g. diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, and higher polyethylene glycols and polypropylene glycols. Particularly suitable are polyethylene glycols and polypropylene glycols having molecular weights 'between 200 and 6000.

Glyoxal is used according to this invention e.g. in the form of technically pure aqueous solutions, which are sold commercially, usually having a glyoxal content of 30 to 40%. Chemical products which liberate glyoxal can also be used, e.g. glyoxal-sodium bisulfite, which is available in pulverulent form and contains about 20% glyoxal. Furthermore partially polymerized glyoxal, which is available in pulverulent form, can also be used.

The present invention is not limited to stabilizing the dimensions of fresh wood or sawn wood, but can be applied also to other wood articles, such as veneer, plywood, laminated wood, particle board, fiberboard and glued wood structures.

In cases where it is preferable'to supply a catalyst to accelerate the formation of cross-linkages, organic or inorganic acids or acid salts may be used, e.g. acetic acid, sulfuric acid, sodium hydrogen sulfate. The treatment with glyoxal and polyalkylene glycol according to this invention is most advantageously carried out by adding both components simultaneously to avoid unnecessary operations, but if desired it is of course possible to carry out treatment with glyoxal and treatment with polyalkylene glycol as separate steps in any order.

In the treatment of wood or wood products according to this invention, it is also possible to supply insecticidal, fungicidal, flame-proofing or coloring substances. It is also possible to combine formulations according to this invention with an introduction of retention-improving agents into the wood, e.g. amino-formaldehyde resin or urea-formaldehyde resin or natural resins. It is also possible to add compositions according to this invention to glues for wood, plywood and other wood products as well as to paints and lacquers for surface treatment of wood or wood products.

The treatment according to this invention can be carried out as a surface treatment or impregnation with polyalkylene glycol and glyoxal. Impregnation can be carried out at normal pressure, superatmospheric pressure or vacuum or as a combined vacuum-pressure impregnating procedure.

It is also possible to supply polyalkylene glycol by treating the wood with an alkylene oxide and effecting -a polymerization thereof in situ in a suitable manner, whereby a polyalkylene glycol is formed by reaction with water present in the wood.

The invention is illustrated by the following working example.

EXAMPLE 1 Beech veneer having a thickness of 2.5 mm. and a moisture ratio of about 50% was immersed for 4 hours in an aqueous solution containing 6% by weight of glyoxal and 15% by weight of polyethylene glycol 1500 (A). Other veneers of the same grade were impregnated with anaqueous solution containing 30% by weight of polyethylene glycol 1500 (B). After drying at 100 C. to moisture ratio, a width shrinkage of 0.9% was found in veneer according to A and 2.0% according to B. Corresponding untreated samples showed a width shrinkage of 8.9%. The absorption of polyethylene glycol in the impregnating period was directly proportional to the concentration thereof in the impregnating liquid, wherefore the amount of polyethylene glycol required could be considerably reduced by the addition of glyoxal and yet an excellent stabilizing effect obtained.

I claim:

1. A method of treating wood to improve dimensional stability and inhibit the development of checks in wood upon drying thereof, which comprises applying to the wood a polyalkylene glycol or glycol-forming material in an amount within the range from about 1 to about by weight glycol, based on the dry weight of the wood, sutficient to cause the wood to swell, and glyoxal or a glyoxal-liberating material and in an amount within the range from about 0.5 to about 20% glyoxal, based on the dry weight of the wood, suflicient to react with itself, the polyalkylene glycol, lignin, and/or cellulose, and impregnating the wood therewith and effecting such reaction of the polyalkylene glycol and glyoxal to improve dimensional stability and inhibit development of checks.

2. A method of treating wood in accordance with claim 1 including the step of drying the wood, after application of the glycol and glyoxal thereto.

3. A method of treating wood in accordance with claim 1 wherein the wood to be treated has a moisture content exceeding the fiber saturation point.

4. A method of treating wood in accordance with claim 1 comprising applying the polyalkylene glycol or glycol forming material and glyoxal simultaneously.

5. A method of treating wood in accordance with claim 1 comprising separately applying the polyalkylene glycol or glycol forming material and glyoxal.

6. A method of treating wood in accordance with claim 1 comprising only surface-treating the wood.

7. A method of treating wood in accordance with claim 1 which comprises applying a vacuum to the wood to be treated, prior to applying the glycol and glyoxal thereto.

8. A method of treating wood in accordance with claim 1 which comprises applying a pressure greater than atmos pheric pressure to the wood to be treated, prior to applying the glycol and glyoxal thereto.

9. A method of treating wood in accordance with claim 1 including, in addition, the steps of applying to the wood a water-soluble glyoXal-reactive material, selected from the group consisting of water-soluble cellulose derivatives, polyvinyl alcohol, partially hydrolyzed polyvinyl acetate, collagen and casein, and effecting reaction of the material with glyoxal, thereby rendering the material less soluble in water.

10. A method of treating wood in accordance with claim 1 which comprises treating the wood with an alkylene oxide, and effecting reaction thereof with itself and with water present in the wood, to form the corresponding polyalkylene glycol in situ in the wood.

References Cited UNITED STATES PATENTS 2,140,981 12/1938 Booty et al 117148 2,572,070 10 /1951 Stamm et al. 117147 2,629,674 2/1953 Ericks 117-148 2,643,236 6/1953 Kropa 26067 2,895,923 7/1959 Kress 26067 2,902,470 9/1959 Kress 26067 3,277,058 1 0/1966 Bastian 26067 3,183,114 5/1965 Liu et a1. 117-147 WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R. 

